The present invention relates in general to tamper-resistant lug nuts and more particularly to tamper-resistant lug nuts designed to secure tires to trailers, trucks and other vehicles. The lug nuts of the present invention may be used to provide tamper-resistant security in other environments.
Whenever separable pieces of equipment are attached together by fasteners, such as tires which are attached to trailers for semi-tractor trucks, there is a possibility that unauthorized persons may remove the attached equipment. A common example of problems associated with such separable equipment is found in the theft of wheels and tires from trailers and truck bodies. If any tires, and including the spare tires can be readily separated from its mounting on the truck, the tires and wheels mounted thereon are more likely to be stolen. Other examples are found in bicycle racks, and motor mounts for boat motors. With the ever increasing costs of such equipment, it becomes still more important to provide a means for quickly, and positively locking pieces of separable equipment in a manner which resists the unauthorized removal thereof, but which permits removal by authorized users without undue struggle.
The prior art has suggested several approaches for fastening separable pieces of equipment together in a manner which purports to be tamper-proof. Such devices generally include a wrench gripping member which is connected to a stud-engaging portion by a frangible or breakable joint. In the application of the lug nut, the stud-engaging portion is threaded onto the stud and tightened to force the separable equipment to the main equipment and when sufficient torque is applied, usually via the wrench, the wrench-engaging portion fractures and shears off, leaving the stud-engaging portion in position. The stud-engaging portion is generally shaped to present a surface which is difficult to grasp with sufficient force to permit the stud-engaging portion to be separated from the stud. Such devices are shown in U.S. Pat. Nos. 1,696,523 and 3,978,761.
However, these prior art devices of the frangible-joint-type nut have a stud-engaging portion which remains exposed after the gripping member has been separated therefrom. Because of the exposed nature of the stud-engaging portion, persons can, given pliers or other equipment of the type usually found in automotive tool boxes, grip the stud-engaging portion with sufficient force to allow the removal of the member from the stud and thus defeat the tamperproof features of the prior art devices.
Other prior art workers have suggested that the frangible joint type lug nut be employed or be shaped in such a manner that the thread-engaging portion is shielded by a shroud-like member which extends above the break-off point so that the shroud prevents the stud-engaging portion from being turned to remove the stud-engaging portion from the stud. Such devices are shown in U.S. Pat. No. 4,037,515 and others. Although such devices are effective in preventing unauthorized removal, the devices similarly handicap the user when authorized removal is desired.
The present invention provides a tamperproof lug nut which can be simply removed, provided one has the appropriate tools and the requisite know-how.